1. Field of the Invention
The present invention relates to a charging control system.
2. Description of the Related Art
Lithium ion secondary batteries (hereinafter simply referred to also as a battery) are secondary batteries using absorbing and storing lithium ions in charging and discharging reactions. The lithium ion secondary battery generates electricity with a higher energy density than a lead battery and a nickel-cadmium battery. In addition, there were few cases where lithium ions, which usually contribute to the charging and discharging reactions in normal uses, precipitate lithium as a single substance on an electrode within the battery. Accordingly, the lithium ion secondary battery has a low possibility of deactivation as a result of drop of lithium from the electrode in the battery as a single substance and a superior repeatability in discharging capacity after repeated charging and discharging cycles, so that a stable cycling characteristic is provided. For these reasons, the lithium ion secondary battery is much expected to have uses, for example, cellular phones, portable electronic devices power sources, emergency auxiliary power sources, power sources for mobile bodies such as a train, a ship, an automobile vehicle, and a two-wheel vehicle, and a power gird such as a smart grid.
However, when the lithium ion secondary battery is overcharged, the battery may be deteriorated, generate heat, ignite, and break, etc. To prevent these troubles, the lithium ion secondary battery is generally provided with a counter measure against the overcharge. The countermeasures are largely divided into two kinds of technologies. One is a technology of previously preventing the overcharging itself. The other is a technology of treating the overcharged secondary battery. There are some types of overcharging protecting technologies such as a potential detecting type, a heat detecting type, and an internal pressure detection type.
As the technology of previously preventing the overcharging itself, JP 9-106835 A discloses a potential detecting type of overcharging protecting technology of making the nonaqueous electrolyte to contain an aromatic compound that polymerizes under a voltage not smaller than the maximum operation voltage previously set. In this technology, the aromatic compound is electrochemically polymerized under the voltage during overcharging, which increases the internal resistance of the battery to suppress the overcharging in the battery. In addition JP 4026587 discloses a technology of making a positive electrode to contain particles such as Cu and Ag. In this technology, these particles solve out from the positive electrode during overcharging and precipitate at the negative electrode in dendrite state to pass through a separator to accelerate minute short-circuiting between the positive and negative electrodes to immediately stop the overcharging.
On the other hand, as the technology of treating overcharged battery, there are two types of overcharging counter technologies, i.e., a heat detection type and an internal pressure detection type. As the heat detection type of overcharging counter measure technology, JP 2009-43485 discloses a technology of utilizing a shutdown function which is inherent to the separator. The separator is generally formed with a porous film serving to prevent short-circuit between the positive and negative electrodes. However, there may be a case where a temperature of the battery extremely increases by for example, an external short-circuiting, and a trouble in charging voltage control function of the battery. In such a case, the separator softens with increase in a temperature of the battery, so that the separator substantially becomes imperforate and does not allow a current to flow, which provides a so-called shut down function. In this technology, the shut down function of the separator can stop the temperature increase of the battery from tens over a hundred degrees to about two hundred degrees and prevent an overcharge current from flowing at a current value not less than the present value. JP 2009-26674 discloses a technology of suppressing progressed overcharging which makes the nonaqueous electrolyte to contain the thermal expansion capsules which expands when the battery temperature increases. When the battery temperature increases due to the overcharging, the thermal expansion capsules expand, which forms spaces where the nonaqueous electrolyte does not exist, so that movement of lithium ions is physically stopped to prevent the progressed overcharging from further progressing.
As the internal pressure detection type of overcharging counter measure technology, JP 2003-59539 discloses an internal pressure releasing mechanism provided in a battery container. In the lithium ion battery using the nonaqueous electrolyte, during a battery trouble such as the overcharging, there may be a case where a large current charging or discharging states may be kept. In such a case, the nonaqueous electrolyte reacts with the active materials of the positive and negative electrodes, which suddenly generates a large quantity of gas within the battery container, so that the internal pressure suddenly increases, and the container may suddenly burst. Accordingly, an internal pressure release mechanism for releasing the internal pressure when the pressure in the battery becomes a predetermined pressure is installed to release the internal pressure at a pressure lower than a burst pressure of the battery. In addition JP 3010781 discloses a technology of releasing a pressure releasing valve before the battery bursts or ignites with a cracked gas generated by decomposition of an addition agent contained in an electrode at a relative low voltage in an initial overcharge stage.
However, for example, in technologies of making additional agents be contained in the electrodes or the nonaqueous electrolytes, materials usable as active material made be contained in the electrodes and components made be contained in the nonaqueous electrolytes may be limited in kind or an ionic conductivity of the nonaqueous electrolytes may be lowered. In addition, for example, in the technology of installing the pressure releasing valve in the battery, an internal structure of the battery becomes complicated or a battery specific capacity may decrease. In other words, to apply the aforementioned technologies, the battery characteristics may be degraded to increase safety of the battery against overcharging.
Accordingly, a technology of applying an overcharging counter measure to a circuit connected to the battery without applying the overcharging counter measure to the inside of the battery is known. JP 2009-72039 discloses that a controller in a low voltage charging circuit measure a voltage battery, and when the battery voltage reaches a forcibly discharging start voltage previously set, a forcible discharging unit forcibly discharge the battery until the battery voltage reach a forcible discharging finish voltage. In addition, JP 2003-284237 discloses that a low voltage diode is connected in series with the battery and when the battery voltage becomes the overcharging voltage, a thermal fuse thermally coupled the low voltage diode is disconnected because a current flowing through the low voltage diode suddenly increases.